Influence of alignment geometry on the global seismic response of tunnel systems

TY - JOUR

T1 - Influence of alignment geometry on the global seismic response of tunnel systems

AU - Mubarak, Ahmad Ghassan

AU - Knappett, Jonathan

AU - Brown, Michael

N1 - © 2026 The Author(s).

PY - 2026/9/25

Y1 - 2026/9/25

N2 - Conventional seismic analyses of tunnels often focus on local seismic actions at specific tunnel sections, overlooking broader effects of asynchronous seismic motion along the wider tunnel alignment which can produce significant amplification of internal forces. This study comparatively investigates the influence of four common tunnel alignment geometries—straight, gradual-L-shaped, tight-L-shaped, and sigmoid—on the global seismic response of long tunnels under synchronous and asynchronous seismic conditions. Nonlinear 3D numerical simulations using the Beam-on-Non-linear-Winkler-Foundation (BNWF) approach were employed considering shallow tunnels running in soil (moraine) and deeper tunnels in rock. The findings reveal that alignment geometry significantly influences the distribution of seismically-induced actions, particularly at locations of stiffness contrast such as tunnel-station connections. Shallow tunnels in soil demonstrated amplified transverse actions at the station-tunnel junctions due to ground-structure stiffness contrast, while deeper tunnels in rock showed more uniform distribution. Non-straight alignments exhibited increased bending moments and shear forces under asynchronous loading conditions as their orientation changed compared to the direction of wave propagation, particularly at shallow depths. The results provide new insight into the mechanisms through which tunnel alignment geometry influences seismic demand under spatially variable ground motion and may assist in the preliminary assessment of alignment-dependent seismic vulnerability in long tunnel systems.

AB - Conventional seismic analyses of tunnels often focus on local seismic actions at specific tunnel sections, overlooking broader effects of asynchronous seismic motion along the wider tunnel alignment which can produce significant amplification of internal forces. This study comparatively investigates the influence of four common tunnel alignment geometries—straight, gradual-L-shaped, tight-L-shaped, and sigmoid—on the global seismic response of long tunnels under synchronous and asynchronous seismic conditions. Nonlinear 3D numerical simulations using the Beam-on-Non-linear-Winkler-Foundation (BNWF) approach were employed considering shallow tunnels running in soil (moraine) and deeper tunnels in rock. The findings reveal that alignment geometry significantly influences the distribution of seismically-induced actions, particularly at locations of stiffness contrast such as tunnel-station connections. Shallow tunnels in soil demonstrated amplified transverse actions at the station-tunnel junctions due to ground-structure stiffness contrast, while deeper tunnels in rock showed more uniform distribution. Non-straight alignments exhibited increased bending moments and shear forces under asynchronous loading conditions as their orientation changed compared to the direction of wave propagation, particularly at shallow depths. The results provide new insight into the mechanisms through which tunnel alignment geometry influences seismic demand under spatially variable ground motion and may assist in the preliminary assessment of alignment-dependent seismic vulnerability in long tunnel systems.

KW - Tunnel liner

KW - earthquake

KW - Hadron colliders

KW - Tunnelling

KW - Seismic Assessment

KW - Numerical modelling

KW - Seismic analysis

KW - Tunnel alignment

KW - Underground structures

UR - https://www.scopus.com/pages/publications/105051504371

U2 - 10.1016/j.tust.2026.108155

DO - 10.1016/j.tust.2026.108155

M3 - Article

SN - 0886-7798

VL - 179

JO - Tunnelling and Underground Space Technology

JF - Tunnelling and Underground Space Technology

IS - 2

M1 - 108155

ER -